I don't myself have an issue with a way of finding out if the user is actually 18

How you go about it is NOT by partnering with a company that wants users data for surveillance reasons, which means you ARE handing off your vulnerable population to god knows where for them to be hurt.

Asylum seekers cannot verify, same with people who have no way to verify themselves.

And what about us folk who want our privacy?

there is a lot wrong with how you are approaching this.